Systems and methods for calibrating the elements of a quantum processor

Abstract

Systems and methods for improving calibration procedures in a quantum processor architecture are described. For example, a dedicated calibration signal source is built into the architecture of the quantum processor for use during calibration. A single calibration signal source is communicatively coupled to many devices in the quantum processor architecture to provide an absolute calibration signal against which various parameters, responses, and/or behaviors of the many devices may be calibrated, either in series or in parallel. The use of a calibration signal source may reduce the time required to calibrate the elements of a quantum processor and/or improve the accuracy/precision of such calibrations.

1 . A quantum processor comprising:
 a plurality of devices, wherein at least a first device in the plurality of devices has a determinable parameter, and wherein the plurality of devices includes a plurality of qubits;   a calibration signal source that is communicatively coupleable to at least the first device in the plurality of devices, wherein the calibration signal source provides a calibration signal; and   a readout system that is communicatively coupleable to at least the first device in the plurality of devices, wherein the readout system reads out a signal that is dependent on both the calibration signal and the determinable parameter of the first device to determine a value for the determinable parameter of the first device.   
     
     
         2 . The quantum processor of  claim 1  wherein the calibration signal source is directly communicatively coupleable to the first device. 
     
     
         3 . The quantum processor of  claim 1  wherein the plurality of devices includes a second device, the second device communicatively coupleable to the first device, and wherein the calibration signal source is directly communicatively coupleable to the second device and indirectly communicatively coupleable to the first device via the second device such that the second device mediates communicative coupling between the calibration signal source and the first device. 
     
     
         4 . The quantum processor of  claim 3  wherein the plurality of devices includes at least a third device, the at least a third device communicatively coupleable to both the second device and the first device, and wherein the calibration signal source is indirectly communicatively coupleable to the first device via the second device and the at least a third device such that the second device and the at least a third device mediate communicative coupling between the calibration signal source and the first device. 
     
     
         5 . The quantum processor of  claim 1  wherein the readout system is directly communicatively coupleable to the first device. 
     
     
         6 . The quantum processor of  claim 1  wherein the plurality of devices includes a second device, the second device communicatively coupleable to the first device, and wherein the readout system is directly communicatively coupleable to the second device and indirectly communicatively coupleable to the first device via the second device such that the second device mediates communicative coupling between the readout system and the first device. 
     
     
         7 . The quantum processor of  claim 6  wherein the plurality of devices includes at least a third device, the at least a third device communicatively coupleable to both the second device and the first device, and wherein the readout system is indirectly communicatively coupleable to the first device via the second device and the at least a third device such that the second device and the at least a third device mediate communicative coupling between the readout system and the first device. 
     
     
         8 . The quantum processor of  claim 1  wherein the quantum processor includes a superconducting quantum processor, the plurality of devices includes a plurality of superconducting devices, the first device is a first superconducting device, the plurality of qubits includes a plurality of superconducting qubits, and the calibration signal source includes a superconducting calibration line formed by a superconducting current path. 
     
     
         9 . The quantum processor of  claim 8  wherein the superconducting calibration line is galvanically coupled to at least one superconducting device in the plurality of superconducting devices. 
     
     
         10 . The quantum processor of  claim 8  wherein the superconducting calibration line is inductively coupled to at least one superconducting device in the plurality of superconducting devices. 
     
     
         11 . The quantum processor of  claim 8  wherein the determinable parameter includes a persistent current of the first superconducting device. 
     
     
         12 . The quantum processor of  claim 8  wherein the plurality of superconducting devices includes at least a second superconducting device that is inductively coupleable to the first superconducting device, and wherein the determinable parameter of the first superconducting device includes a mutual inductance between the first superconducting device and the second superconducting device. 
     
     
         13 . The quantum processor of  claim 12  wherein the second superconducting device is a superconducting qubit. 
     
     
         14 . The quantum processor of  claim 1  wherein the plurality of devices includes at least a second device having a determinable parameter, the calibration signal source is communicatively coupleable to the at least a second device, and the readout system is communicatively coupleable to the at least a second device, wherein the readout system reads out a signal that is dependent on both the calibration signal and the determinable parameter of the at least a second device to determine a value for the determinable parameter of the at least a second device. 
     
     
         15 . The quantum processor of  claim 14  wherein the calibration signal source is communicatively coupleable to every device in the plurality of devices. 
     
     
         16 . The quantum processor of  claim 1  wherein the first device is a qubit. 
     
     
         17 . The quantum processor of  claim 1  wherein the plurality of devices includes at least one of: a qubit, a latching device, a coupling device, a readout device, and a programming device; and wherein the first device is selected from the group consisting of: a qubit, a latching device, a coupling device, a readout device, and a programming device. 
     
     
         18 . A method of calibrating at least one device in a quantum processor, wherein the quantum processor comprises a plurality of devices including at least a first device having at least a first determinable parameter, a calibration signal source that is communicatively coupleable to the at least a first device, and a readout system that is communicatively coupleable to the at least a first device, the method comprising:
 applying a calibration signal to the quantum processor via the calibration signal source;   communicatively coupling at least a portion of the calibration signal from the calibration signal source to the first device;   reading out a signal that is dependent on both the calibration signal and the first determinable parameter of the first device via the readout system; and   determining a value for the first determinable parameter of the first device based at least in part on the signal that is read out via the readout system.   
     
     
         19 . The method of  claim 18  wherein the calibration signal source is directly communicatively coupleable to the first device such that communicatively coupling at least a portion of the calibration signal from the calibration signal source to the first device includes communicatively coupling at least a portion of the calibration signal directly from the calibration signal source to the first device. 
     
     
         20 . The method of  claim 18  wherein the quantum processor includes at least a second device, the at least a second device communicatively coupleable to the first device, and wherein communicatively coupling at least a portion of the calibration signal from the calibration signal source to the first device includes communicatively coupling at least a portion of the calibration signal from the calibration signal source to the at least a second device and communicatively coupling at least a portion of the calibration signal from the at least a second device to the first device such that the at least a second device mediates communicative coupling between the calibration signal source and the first device. 
     
     
         21 . The method of  claim 18  wherein the readout system is directly communicatively coupleable to the first device such that reading out a signal that is dependent on both the calibration signal and the first determinable parameter of the first device via the readout system includes reading out at least a portion of the signal directly from the first device via the readout system. 
     
     
         22 . The method of  claim 18  wherein the quantum processor includes at least a second device, the at least a second device communicatively coupleable to the first device, and wherein reading out a signal that is dependent on both the calibration signal and the first determinable parameter of the first device via the readout system includes communicatively coupling at least a portion of the signal from the first device to the at least a second device and reading out at least a portion of the signal from the at least a second device via the readout system such that the at least a second device mediates communicative coupling between the first device and the readout system. 
     
     
         23 . The method of  claim 18  wherein the quantum processor includes a superconducting quantum processor, the first device includes a first superconducting device, the calibration signal source includes a superconducting calibration line formed by a superconducting current path, the quantum processor includes at least a second superconducting device, and the first determinable parameter of the first device includes a mutual inductance between the first superconducting device and the second superconducting device, and wherein:
 applying a calibration signal of a known value to the quantum processor via the calibration signal source includes applying a calibration signal of a known value to the superconducting quantum processor via the superconducting calibration line; 
 communicatively coupling at least a portion of the calibration signal from the calibration signal source to the first device includes communicatively coupling at least a portion of the calibration signal from the superconducting calibration line to the first superconducting device; 
 reading out a signal that is dependent on both the calibration signal and the first determinable parameter of the first device via the readout system includes reading out a signal that is dependent on both the calibration signal and the mutual inductance between the first superconducting device and the second superconducting device via the readout system; and 
 determining a value for the first determinable parameter of the first device based at least in part on the signal that is read out via the readout system includes determining a value for the mutual inductance between the first superconducting device and the second superconducting device based at least in part on the signal that is read out via the readout system. 
 
     
     
         24 . The method of  claim 23  wherein at least one of the first superconducting device and the second superconducting device is a superconducting qubit. 
     
     
         25 . The method of  claim 18  wherein the quantum processor includes a superconducting quantum processor, the first device includes a first superconducting device, the calibration signal source includes a superconducting calibration line formed by a superconducting current path, and the first determinable parameter of the first device includes a persistent current of the first superconducting device, and wherein:
 determining a value for the first determinable parameter of the first device based at least in part on the signal that is read out via the readout system includes determining a value for the persistent current of the first superconducting device based at least in part on the signal that is read out via the readout system. 
 
     
     
         26 . The method of  claim 18  wherein the quantum processor includes at least a second device having a first determinable parameter, the calibration signal source is communicatively coupleable to the at least a second device, and the readout system is communicatively coupleable to the at least a second device, the method further comprising:
 communicatively coupling at least a portion of the calibration signal from the calibration signal source to the at least a second device; 
 reading out a signal that is dependent on both the calibration signal and the first determinable parameter of the at least a second device via the readout system; and 
 determining a value for the first determinable parameter of the at least a second device based at least in part on the signal that is dependent on both the calibration signal and the first determinable parameter of the at least a second device that is read out via the readout system. 
 
     
     
         27 . The method of  claim 18  wherein each device in the plurality of devices has at least one respective determinable parameter, the calibration signal source is communicatively coupleable to each device in the plurality of devices, and the readout system is communicatively coupleable to each device in the plurality of devices, the method further comprising:
 communicatively coupling at least a portion of the calibration signal from the calibration signal source to each device in the plurality of devices; 
 reading out a respective signal from each device in the plurality of devices via the readout system, wherein each respective signal is dependent on both the calibration signal and the respective determinable parameter of the respective device from which the signal is read out; and 
 determining a respective value for the respective determinable parameter of each respective device based at least in part on each respective signal that is read out via the readout system. 
 
     
     
         28 . The method of  claim 18  wherein the at least a first device has a second determinable parameter, the method further comprising:
 determining a value for the second determinable parameter of the at least a first device based at least in part on the value for the first determinable parameter of the at least a first device.